The use of laser beams is the basis for a great number of applications such as, e.g., medical surgery methods, the investigation and machining of materials, or the investigation and manipulation of biological samples in, for example, laser scanning microscopy. The instruments used in many of these applications are supplied with laser radiation by means of optical waveguides. For this purpose, the laser beam must, after its exit from the radiation source or another optical component, be coupled into the optical waveguide by means of a coupling device and coupled out again at the site of application, i.e. in the respective instrument, by means of another coupling device. In the instrument, the laser beam propagates as a free, unguided beam—i.e. not within an optical waveguide—and is used in the respective application. To keep radiation losses and imaging aberrations as low as possible and to maintain the highest possible beam quality during coupling into the instrument, the optical waveguide must be very accurately positioned relative to the coupling optics. Accordingly, during its outcoupling, the beam must be introduced into the respective instrument with high accuracy with regard to the direction and position of beam propagation. Such coupling devices, as a rule plug connections consisting of plug-and-socket pairs, are internationally classified in four quality grades denoted A through D. The higher the quality, the higher are the effort and expense in manufacturing, as a rule.
All coupling devices known in prior art have in common that the disconnection and subsequent remaking of such an optical waveguide connection, at least in cases where the optical waveguide is plugged to another instrument or where a different optical waveguide, even of the same type, is fixed to the same instrument, laborious readjustments are always necessary unless one would accept considerable performance and quality losses of the transmitting light or beam maladjustments. Disconnection of an optical waveguide plug connection may be necessary, for example, in order to make possible a simple change of the light sources—e.g., the use of a laser of different wavelength—and/or of the feeding points—e.g., feeding the light to a different instrument. In prior art there exist various products in which mounting and adjusting mechanisms are combined with focusing optics. The necessary—maximally six—degrees of freedom are set by means of various operating principles and adjusting strategies. All solutions known in prior art, however, require a great deal of adjustment work, which during integration into the respective instrument has to be done, as a rule, by trained service staff on the site of installation. Nevertheless, the coupling afterwards will not be fixed well enough to ensure a lasting, stable quality of the beam coupling or outcoupling.
DE 198 40 935 B4, for example, describes an end piece for optical fibers, which serves for coupling laser radiation into or out of an optical fiber. As shown in FIG. 11 of the document cited, the end piece is connected to the housing that accommodates the pumping source, via a mount. The end piece is provided with one or several outer fitting surfaces, which serve(s) as reference surface(s) for aligning the beam of light. These fitting surfaces are all provided on the circumference around the end piece. The end piece is then plugged into the housing so that its fitting surfaces bear against the mount. The end piece is further provided with means for adjusting the position of the optical fiber relative to the fitting surfaces. By means of these adjusting means, e.g., screws, the optical fiber is aligned relative to the cylindrical or conical reference surfaces. Fitted to the front end of the end piece is a collecting lens for coupling the radiation in or out. If the end piece is disconnected from the housing and inserted into another housing of the same design, it is true that the adjustment of the optical fiber relative to the fitting surfaces is maintained, but there is the added problem of correctly inserting the fitting surfaces into the mount of the housing so that the alignment of the of the end piece in the housing is optimum. As the reference or fitting surfaces and the mounts are of cylindrical or conical shape, inevitable manufacturing tolerances bring it about that, as the end piece is simply inserted into the housing, the symmetry axes of end piece and housing form a small angle between them, as a rule. Even though the deviations are very small, they will result in quality losses. While an exactly parallel alignment will be possible, as a rule, this will take a lot of time and sensitive dexterity.
Another device for adjusting an optical fiber is described in DE 32 38 049 C1. Here, a housing contains a focusing element such as a collimating lens; the adjusting devise essentially consists in an adjusting ball with a through-hole accommodating the optical fiber. The adjusting ball is bearinged so as to be not only rotatable but also translatable parallel to the optical axis of the collimating lens. This allows the exit surface of the optical fiber to be positioned at the focus of the collimating lens so that the best possible coupling or outcoupling is achieved. Once adjustment has been accomplished, the guide sleeve or the housing can be connected with a suitable other element allowing the beam to be utilized. In this case, the outer surfaces of the guide sleeve serve as fitting surfaces, so that, when such a connection is made or disconnected, the Problem of readjustment occurs just as in case of the previously cited document.
The same problem occurs with the end piece described in U.S. Pat. No. 6,796,720 B2: An optical fiber is inserted into a ferrule; this ferrule is plugged into the end piece and aligned there axially and radially by means of adjusting screws relative to a collimating lens fitted to the front end of the end piece. The end piece, of cylindrical outer shape, can, in turn, be plugged into a corresponding mount.
A different arrangement, intended to bring about the optical coupling or outcoupling of radiation with the best possible efficiency, is described in U.S. Pat. No. 6,925,234 B2. Unlike the arrangements described before, in which fiber and lens were arranged in one and the same end piece, the last-mentioned arrangement accomplishes a high flexibility with regard to the relative adjustment of fiber and lens, in that the end piece consists of two parts. In a first part of the plug, the fiber is fixed in a ferrule, whereas the lens is rigidly arranged in a second part of the plug. Then the first and the second part of the plug can be rigidly connected, e.g. by means of screws. However, the first part of the plug, which accommodates the fiber, is designed in such a way that, despite the rigid connection of the two parts of the plug, a flexible axial and radial adjustment of the position of the exit surface of the fiber is possible by means of adjusting screws. This possible because the first part of the plug, although one piece, itself consists, in a way, of two segments, with enough material being removed between these two segments as to form a kind of elastic hinge. The end piece or the multipart plug has a cylindrical outer shape, so that, when a connection with an instrument intended to utilize the radiation is disconnected or remade, the same problems with adjustment occur as with the arrangements described before. As the alignment of the fiber end surface and the lens are effected via adjustments on the single-piece elastic hinge, such adjustment is rather laborious.